The demand for hydrogen peroxide solutions having high purity sufficient for use in the electronics industry has been increasing with the advancement of DRAM (dynamic random-access memory) integration density. The latest demand is to reduce metallic impurity contents to several ppb (part per billion) and acid radical impurity contents to several tens ppb at the most. Hydrogen peroxide solutions themselves are relatively stable and, with high purity, need no stabilizer for prevention of decomposition. For the time being, however, since hydrogen peroxide solutions are produced by alkylanthraquinone autoxidation, they contain trace amounts of metallic impurities and are thereby somewhat unstable.
JP-A-1-153509 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses a process in which a crude hydrogen peroxide solution is treated with an anion exchange resin having adsorbed thereon a chelating agent. It is received that a chelating compound is coordinated on a dissolved metallic compound having a catalytic decomposition activity to stabilize the metallic compound thereby inhibiting the catalysis of the metallic compound. Such a stabilizing compound, when added to the crude solution, must be removed afterward by any known purification system to finally obtain a high purity hydrogen peroxide solution. While the above-described process is satisfactory as far as the removal of the four kinds of metallic ions mentioned is concerned, it encounters with difficulty in removal of acid radicals. The chelating agents disclosed in this patent, for example, ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and diethylenetriaminepentaacetic acid (DTPA), have an acid dissociation constant pKa in the first stage of 2.0, 1.9, and 2.1, respectively (see The Chemical Society of Japan (ed.), KAGAKU BINRAN KISO-HEN II, 2nd Ed., p. 993, Maruzen, Tokyo (1975)).
On the other hand, the dissociation constant of phosphoric acid in the first stage is 2.15, very close to those of the above-described chelating agents. In other words, the chelating agents do not act as a weak acid with respect to phosphoric acid and therefore have difficulty in removing a phosphoric acid radical. Further, the patent states that the ratio of chelating agent to functional group of the anion exchange resin is not always 1:1 and may be less in some cases. In this case, however, the residual counter ion is a chloride ion, which is unsuitable for displacement of a dilute phosphoric acid radical.
JP-B-35-16677 (the term "JP-B" as used herein means an "examined published Japanese patent application") discloses that a hydrogencarbonate type anion exchange resin evolves only carbon dioxide. However, seeing that the composition analysis of the gas evolved revealed the presence of oxygen gas, this type of anion exchange resin appears to catalyze hydrogen peroxide decomposition. Moreover, considerable gas evolution also occurs with a carbonate type anion exchange resin. Thus, the process proposed is unsatisfactory in securing safety in purification of hydrogen peroxide solutions.
U.S. Pat. No. 3,297,404 and JP-B-35-16677supra suggested the advantage of a hydrogencarbonate type strongly basic anion exchange resin in removal of metallic anions from hydrogen peroxide solutions but give no reference to the increase of decomposing activity with the amount of a hydrogen peroxide solution treated. Similarly, U.S. Pat. No. 3,294,488 describes usefulness of a hydrogencarbonate type strongly basic anion exchange resin in removal of a carboxylic acid radical, giving no reference to the increase of decomposing activity.